Coloring of paper with sulphur colors



' gog about 170 tol90 Patented Jan. 14, 1941 UNITED STATES COLORING OF PAPER WITH SULPHUR COLORS Edwin R. Laughlin, Penns Grove, N. J., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a. corporation of Delaware No Drawing. Application November 29, 1938, Serial No. 242,898

8 Claims.

This invention relates to the manufacture of colored paper and especially to the coloring of cellulosic fibres with sulphur colors while the fibres are in aqueous medium.

Paper has heretofore been colored with sulphur colors but in those processes, quantities of hydrogen sulphide were evolved when the sodium sulphide in the dye solutions was neutralized.

Alum was customarily used for neutralization.

Because of the poisonous and offensive properties of hydrogen sulphide and the difficulties and cost of disposing of the poisonous gas, the use of sulphur dyes for making colored paper has not been as extensive as would be expected in a view of the superior properties of the sulphur colors for coloring paper fibres. It is therefore desirable that processes be provided for coloring paper with sulphur colors which will avoid the production and evolution of the harmful and poisonous hydrogen sulphide gas during the process.

It is among the objects of the invention to provide satisfactory improved processes for coloring paper with sulphur dyes. Another object of the invention is to provide new processes for applying sulphur colors to paper fibres in the beater. Other objects of the invention will "be apparent from the following more detailed description.

The objects of the invention are accomplished in general by adding a basic solution ofreduced sulphur dye which contains the sulphide of an alkali metal or ammonia to the wet fibres or an aqueous suspension of the paper fibres, as for r example the mixture in the beater. Then a salt of a metal which forms an insoluble sulphide in basic and neutral solutions is applied. A quantity of the metal which is at least equivalent to the sulphur present as soluble sulphide is added 40 and all the sulphide is thereby precipitated as the sulphide ofthe metal. The soluble salt is added until lead acetate paper will give no test for soluble sulphide. The stock is subsequently treated in the usual way to finish the paper.

r The invention will bemore fully set forth in the following more detailed description which includes examples that are given as illustrative embodiments of the invention and not as limitations thereof.

Example I In preparing a sized paper, five pounds of 60% sodium sulphide were dissolved in about three gallons of water and added to a beater charge which contained 1000 pounds of kraft stock at 55 5% consistency.

Sulfogene Carbon M (C. I. 9'78) was prepared in reduced form by dissolving 30 pounds of the dyestuif in a solution containing pounds of 60% sodium sulphide in ten gallons of water at F. and stirring at this temperature until the sulphur black was dissolved.

The solution of reduced sulphur color was then added to the beater and thoroughly mixed. When the paper stock was dyed, a water solution containing about pound of zinc chloride (99%) was added to the mixture for each pound of 60% sodium sulphide previously used in the reduction of the dye and that added to the mix-' ture in the beater. In this charge 15 pounds of 99% zinc chloride dissolved in five gallons of water were added and thoroughly mixed with .the rest of the charge in the beater. This addition made the mixture in the beater approximately neutral and formed an amount of zinc sulphide precipitate equivalent to all the sulphur capable of forming hydrogen sulphide upon acidification. The residual solution in the beater did not darken lead acetate paper.

After the precipitation of the sulphide pounds of rosin size were thoroughly mixed into the contents of the heater and then 20 pounds of alum were added to fix the size. During this operation no hydrogen sulphide was evolved.

The material in the beater was then processed with paper making machinery and paper was made in the usual way. During the processing of the colored pulp the dissolved salts and some zinc sulphide were eliminated. Whatever small amount of nearly white zinc sulphide was retained by the paper did not materially affect the color of the paper.

In accordance with the process as heretofore practiced, the same proportions of paper stock, sodium sulphide and reduced sulphur color were used as in Example 1. Dry papermakers alum was then added to the beater until the mixture was neutral but no zinc salt was added. This resulted in a copious evolution of hydrogen sulphide. About 1 pounds of alum were required for each pound ofsodium sulphide (60%)'in the wet mixture. The stock was then sized by adding rosin size and alum as hereinbefore described, and the stock was then formed into paper. The requirements of the process were excessive in alum or other neutralizing agent and the hazard and nuisance from poisonous hydrogen sulphide gas could not be avoided whether or not rosin size and alum fixer were subsequently added.

Example II Example III Sized colored paper was prepared in accordance with the procedure of Example I except that the sodium sulphide which was added to no the beater charge before adding the dyestuff was omitted. In this case a smaller amount of zinc chloride was needed to combine with the sulphide since the only sulphide present was that associated with the reduced preparation of Sulfogene Carbon M.

Example IV A 1000 pound charge of unbleached kraft (6% consistency) containing 5 pounds of sodium sulphide fused flakes) was mixed in the beater with a. solution of 20 pounds of the blue sulphur color corresponding to C. I. 959 which had been reduced with 20 pounds of sodium sulphide (60% fused flakes) in 20 gallons of hot water. After thoroughly mixing, 20 pounds of zinc chloride were added in water solution. Du Pont Paper Blue S (a soluble form of Prussian blue) was then added to the heater in dry form. After mixing to distribute the color, the stock was sized by 20 pounds of rosin size and then 30 pounds of alum. By forming the pulp in the usual way with paper making machinery a blue paper was produced and no hydrogen sulphide was liberated.

Example V A 1000 pound charge of rag blotting stock (5% consistency) containing 5 pounds of sodium sulphide (60% fused flakes) was mixed in the beater with a solution of the brown sulphur color corresponding to C. I. 935 which had been reduced with 18 pounds of sodium sulphide (60% fused flakes) in 20 gallons of hot water. After thoroughly mixing, 20 pounds of zinc chloride were added in solution and thoroughly mixed. Then 9 pounds of Pontamine Fast Orange MRL (C. I. 621) were added in dry form, followed by 100 pounds of salt. After throughly mixing and heating to 120 F., 7 pounds of alum were added. A brow-n blotting paper was made from this dyed pulp by processing in the usual way.

The Pontamine Fast Grange MRL can be added in solution if desired.

Example VI A 1000 pound charge of unbleached sulphite Pulp (EH/2% consistency) containing 5 pounds of sodium sulphide fused flakes (60%) was mixed in the beater with a. solution of Sulfogene Carbon M. grains (0. I. 978) which had been reduced with 18 pounds of sodium sulphide flakes (60%) in 15 gallons of hot water. After a thorough mixing 35 munds of copper sulphate crystals were added in water solutiorT and thoroughly.

mixed with the charge. Asolution of 3 pounds of Du Pont'Methyl Violet NE (C. I; 680) and a solution of 1 pound of Du Pont Victoria Green S. C. (C. I. 657) were added separately and thoroughly-mixed. The pulp was sized by-add ing 25 pounds of rosin size and 35 pounds of alum. The paper made from this dyed pulp was black and no hydrogen sulphide was evolved in [the process.

In the foregoing examples it was found that the small amount of almost colorless zinc sulphide retained in the paper did not materially affect the color. In cases where colored sulphides are formed by adding salts of other metals, such as copper, the colored sulphide is sometimes advantageous in that its color lends character or intensifies the dyeing. For example, the presence of a small amount of copper sulphide is not disadvantageous in dyeing the paper with a sulphur black since the retained sulphide tends to jet and deepen the shade of the pulp. Except as noted, the presence of the metal sulphide which is retained by the paper has no effect other than an equivalent amount of other filler would have.

In general, any soluble salt of any metal which forms insoluble sulphides in neutral and basic solutions and which sulphides are not soluble in solutions having acidity equivalent. to solutions acidified with aluminum sulphate to a pH value of about 7 to 4, can be used instead of zinc chloride, such as the soluble salts of lead, copper, cadmium, nickel, mercury, bismuth and iron. It is preferred to use the metal salts of nonoxidizing, inorganic and organic acids, such as the chlorides, sulphates and acetates, but others can be used. A variety of selection can be made where a metal salt other than a zinc salt is added in order to provide a residue of colored sulphide associated with the pulp and intended to alter the hue and occasionally the strength of the dyeing on the finished paper. For example, retained lead or copper sulphide tends to deepen the shade of a black dye and .a yellow sulphide tends to change the character of variously colored dyeings.

Any sulphur dye can be used in the practice of the present invention and more or less soluble sulphide salt may be present in the bath containing the reduced dye. Instead of sodium sulphide any alkali metal sulphide or ammonium sulphide can be used. After the sulphur in the soluble sulphide is transformed into an insoluble sulphide more or less acid can be added without liberating hydrogen sulphide if the solution is alkaline and it is desired to vary the pH value of the solutions present. For this purpose any neutralizing agent can be used. Bases can also be added for the purpose of adjusting the solutions. The expedient may be conveniently utilized in the manufacture of unsized papers when it is desired to run the beater mixture near neutrality.

Satisfactory results are obtained with any kind of paper fibres, for example, kraft, soda. sulphite, rag, ground wood or alpha pulp, either bleached or unbleached.

In manufacturing sized and unsized products any basic or direct dye can be used in conjunction with-the sulphur colors, and any of the acid or pigment colors are also used in conJunction with the sulphur colors to color sized materm]. The acid, basic, direct or pigment color is preferably but not necessarily added to the pulp mixture after neutralization since some of these colors are affected by alkaline solutions and the full tinctorial strength of the dyes can be developed to the best advantage when they are added in neutral solutions. As illustrations of basic, direct, acid and pigment colors which have given satisfactory results in conjunction with sulphur colors the following are mentioned: the basic colors Du Pont Saframine T Extra (C. I. 841) and Du Pont Methylene blue ZX (C. I. 922), the direct colors Du Pont Brilliant Paper Yellow Conc. (C. I. 364), Pontamine Fast Scarlet 4 B S (C. I. 327), Pontamine Black E (C. I. 581) and Pontamine Deep Blue B H Conc. (C. I. 401), the acid'colors Du Pont Metanil Yellow Conc. (C. I. 138) and the red azo dye made by coupling diazotized p-amino-acetanilide with acetyl-J acid; and the yellow pigment made by coupling diazotized meta-nitro-para-toluidine with aceto acetanilide; chrome yellow, iron oxide and many others.

The invention provides a method whereby the valuable, desirable and inexpensive sulphur dyes can be utilized in a safe and economical manner to color paper pulp and other cellulose fibres without exposing the operators to the inconvenience and dangers of hydrogen sulphide. While the process utilizes a reagent to form an insoluble sulphide which is not commonly used in the coloring of cellulose fibres the use of such compound displaces a neutralizing agent which was heretofore employed, such as alum. While the improved process is operated at a slight additional cost over the conventional methods, it eliminates the health hazard of the conventional methods and provides a new means for varying the strength and depth of the dyeings made with sulphur dyes.

The fibres which are colored in accordance with the invention may be used to make many varied types of paper products which are in sheet'form as well as those which are not in sheet form, such as molded products. The formed or the unformed dyed fibres may be treated with zinc chloride to produce vulcanized fiber or .with parchmentizing agents, such as sulphuric acid. A great variety of, manufactured products may be made by mixing, impregnating or otherwise treating the formed or unformed colored fibres with other agents such as rubber latex, natural and synthetic resins, gums and other treating agents.

Since from the foregoing description of the invention it will be apparent to those skilled in the art that various other embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that no limitations are intended except those which are specifically recited in the annexed claims or are imposed by the prior art.

I claim:

1. The process of manufacturing colored cellulosic fibres which comprises suspending the fibres in water, adding to the water suspension of the fibres a basic solution of a soluble sulphide and a reduced sulphur dyestufl? containing the sulphide to make the pulp mixture basic, adding to said mixture a water soluble salt of a metal which forms insoluble sulphides in neutral and alkaline solutions, said metal being one which forms a sulphide that is insoluble in a solution having a pH value equivalent to the pH value between 4 and 7 which is produced by addition of aluminum sulphate to a hydrous cellulosic pulp, said metal salt being .added until all the soluble sulphide is transformed into an insoluble sulphide of the metal and before any quantity of acid capable of liberating hydrogen sulphide from said basic solution is added thereto.

2. The process of manufacturing colored cellulosic fibres which comprises suspending the fibres in water, adding a basic solution of a soluble sulphide and reduced sulphur color containing the sulphide to make the pulp mixture basic, adding to said mixture a water soluble salt of a metal which forms insoluble sulphides in neutral and alkaline solutions, said metal being one which forms a sulphide that is insoluble in a solution having a pH value equivalent to the pH value between 4 and 7 which is produced by addition of aluminum sulphate to .ahydrous cellulosic pulp, said metal salt being added until all the soluble sulphide is transformed into an insoluble sulphide of the metal and before any quantity of acid capable of liberating hydrogen sulphide from said basic solution has been added, and then adding to said mixture a color of the class consisting of basic, direct, acid and pigment dyes.

3. The process. of manufacturing colored cellulosic fibres which comprises suspending the fibres in water, adding to the water suspension of the fibres a solution of an alkali metal sulphide and a suflicient quantity of a reduced sulphur dyestufi to dye the fibres and make the pulp mixture basic, adding to said mixture a water soluble salt of a metal which forms insoluble sulphides in neutral and alkaline solutions, said metal being one which forms a sulphide that is insoluble in a solution having a pH value between 4 and 7 when produced by addition of aluminum sulphate. to a hydrous cellulosic pulp, said metal salt being added until all the soluble sulphide is transformed intoan insoluble sulphide of the metal and before any quantity of acid c2 pable of liberating hydrogen sulphide from said basic solution is added thereto.

In the process of manufacturing paper from cellulosic fibres, the steps which comprise suspending the fibres in water, adding to the water suspension of the fibres a sufficient quantity of a sodium sulphide and a reduced sulphur dyestufi to dye the fibres and make the pulp mixture basic, adding to said mixture a water soluble salt of a metal which forms insoluble sulphides in neutral and alkaline solutions, said metal being one which forms a sulphide that is insoluble in a solution having a pH value between 4 and 7 when produced by addition of aluminum sulphate to a hydrous cellulosic pulp, said metal salt being added until all the soluble sulphide is transformed into an insoluble sulphide of the metal and before any quantity of acid capable of liberating hydrogen sulphide from said basic solution is added thereto.

5. The process of manufacturing colored cellulosic fibres which comprises suspending the fibres in water, adding to the water suspension of the fibres a basic solution of a soluble sulphide and a reduced sulphur dyestuff containing the sulphide to make the pulp mixture basic, adding to said mixture a water soluble lead salt, sufficient of said salt being added to transform all the soluble sulphide into an insoluble sulphide of the metal and said addition being made before any quantity of acid capable of liberating hydrogen sulphide from said basic solution is added thereto.

6. The process of manufacturing colored cellulosic fibres which comprises suspending the fibres in water, adding to the Water suspension of the fibres a basic solution of a soluble sulphide and a reduced sulphur dyestufi containing the sulphide to make the pulp mixture basic, adding to said mixture a water soluble copper salt, suflicient of said salt being added to transform all the soluble sulphide into an insoluble sulphide of the metal and said addition being made before any quantity of acid capable of liberating hydrogen sulphide from said basic solution is added thereto.

7. The process of manufacturing colored cellulosic fibres which comprises suspending the fibres in water, .adding to the water suspension of the fibres a solution of sodium sulphide and suflicient of a reduced sulphur dyestuff to dye the fibres and make the pulp mixture basic, and then adding zinc chloride to said basic mixture until all soluble sulphide is transformed into an insoluble sulphide.

8. The process of manufacturing colored cellulosic fibres which comprises suspending the fibres in water, adding to the water suspension of. the

metal and said addition being made before any quantity of acid capable of liberating hydrogen sulphide from said basic soiutiqn is added thereto.

EDWIN R. LAUGI-KIN. 

